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‘World’s first off-road solar SUV’ just drove across Morocco powered only by the sun
(edition.cnn.com)
This is a most excellent place for technology news and articles.
you can make the engine more efficient, but at some point there is a minimum amount of energy needed to get the thing moving and they are already quite close to fully efficient. To reduce energy needed any further you can make the car lighter, but that obviously cannot be improved indefinitely.